Forecasting Economic Damages from Storm Surge Flooding in the Tantramar Region of New Brunswick

Building off previous research which estimated changes in storm surge flood heights from projected changes in sea-level rise, Green Analytics partnered with Mount Allison University in 2012 to conduct a comparative analysis of economic damages associated with storm surge related coastal flooding under future climate change scenarios in the community of Sackville, New Brunswick and identified potential implications for community adaptation strategies. The Tantramar region of South-East New Brunswick is a coastal zone subject to strong tidal forces from the upper Bay of Fundy, and relies on an approximately 33-km dyke system to protect the Town of Sackville, an interprovincial railway and highway, and surrounding agricultural lands. In the Tantramar region, one of the larger climate change related threats is changing flood risk associated with increased sea-level rise. The extent to which communities, such as the Town of Sackville and the Tantramar region, should develop adaptation plans designed to address this risk depends on the anticipated costs of future flooding events. Building off the research conducted by Daigle (2012), which estimated changes in storm surge flood heights from projected changes in sea-level rise, the current research was able to examine the potential costs of flood damages to the Town of Sackville and surrounding region for four economic sectors, including: residential, commercial/industrial, agriculture, and public.

Understanding and Assessing Impacts

The issue of sea-level rise and its implications for coastal communities in New Brunswick has become a
growing concern as climate change science continues to advance our understanding of the issue. Previous work, supported by the Atlantic Climate Adaptation Solutions Association (ACASA) and Mount Allison University, documented the significant flood risks facing the Tantramar region. Recently published sea-level estimates for an 8.9m, 1-in-10 yr. storm surge, for instance, could overtop approximately 90% of the existing dyke system and temporarily inundate 20% of the town of Sackville, New Brunswick. In an effort to better understand the economic costs associated with climate-change related flood risk, this study was conducted as part of a partnership between Green Analytics and Mount Allison University, and was funded by ACASA, Mount Allison University and the Social Sciences and Humanities Research Council of Canada (SSHRC). Sea level estimates were obtained from Daigle (2012) and combined with assets-at-risk (e.g., residences, warehouses, etc.) within a geographic information system (GIS) housed at Mount Allison University. Using a regime of climate-change scenarios and known assets-at-risk, three objectives were defined to:

  1. characterize the existing (or baseline) potential damages associated with storm surge flooding;
  2. characterize how these potential damages are likely to change with predicted increases in climate change-related sea-level rise; and
  3. demonstrate how adaptation scenarios can be analyzed for their effectiveness in reducing exposure to flood damages.

For this case study, the cost of potential damages of flooding in Sackville were assessed by economic sector, including: residential, commercial/industrial, agriculture, and public. Damage estimates were then organized to depict flood damages for a range of climate change futures and adaptation scenarios, ultimately forming the comparative analysis.

Identifying Actions

To evaluate the potential for community adaptation to offset the expected costs, authors drew on the input from local stakeholders in combination with general flood mitigation literature to define four adaptation strategies. To demonstrate how communities, such as the Town of Sackville and Tantramar region, assess the influence of adaptation strategies a series of adaptive strategies or options were identified. Previous research explored some adaptations through a stakeholder engagement process. Feedback from the stakeholder focus group held on April 19, 2011 identified several adaptation options, for example: Move sewage treatment plant, increase the height of dykes, and relocate residents and businesses. These suggestions formed the starting point for scoping the adaptation strategies. Drawing on input from local stakeholders in combination with general flood mitigation literature, the research team outlined three adaptation scenarios for analysis in addition to the ‘status quo’ or baseline scenario as a starting point for the Tantramar region to consider: Status Quo, Dyke Top-up, Relocation, and Natural Infrastructure. To capture local knowledge, expertise, and policy implications, a half-day workshop was held on May 31, 2012 to present preliminary findings and discuss the feasibility, both physically and politically of each adaptation scenario. The workshop brought together a select group of local experts and stakeholders representing a range of knowledge areas including: local policy, hydrology, agriculture, dyke management, and wetland management. Each scenario was explored in detail, discussing their effectiveness to reduce flood risk, policy implications, and expected costs. The general consensus was centred on the timing of scenarios. For instance, dyke top-up was considered the most effective short-term solution, allowing time to develop longer-term strategies and policies necessary to provide more permanent protection from flood vulnerability.

Implementation

As a result discussions with stakeholders, the following adaptation scenarios were redefined to the following:

  1. Status quo (baseline), assuming that no mitigation or adaptation measures are undertaken and all system changes can be attributed to climate change.
  2. Dyke top-up, involving a 1 m increase in dyke height from 8.5 m to 9.5 m above sea level, a 2-3year delay to coordinate policy and secure funding, and a 5 year work plan resulting in completion by 2020.
  3. Relocation, where highly vulnerable properties are relocated to areas of limited vulnerability. This scenario does not imply a forced relocation or expropriation. Rather, it captures the potential avoided damages that would result if relocation occurred. Such relocation could be supported through a range of policy options including tax incentives and strategic land-use planning.
  4. Mixed strategy, involving both dyke top-up and relocation.

For the purpose of this analysis it was assumed that it would take 13 years to coordinate policy and funding to support this strategy; and relocation would commence in 2025, and would not be complete until 2045.  There are many possible adaptation strategies that could be explored. The strategies chosen for this project are meant to showcase the two likely to provide significant benefits in terms of damage costs avoided. Also, due to data limitation implantation costs could not be calculated in much detail.

Outcomes and Monitoring Progress

A common approach to assess the direct impacts involves the use of something referred to as a “stage damage curve”, which relates the depth of floodwater to the expected severity of the damage. Fortunately, the relationship between flood depth and damage to a given asset is relatively consistent, justifying the use of already established stage damage curves produced by the U.S. Army Corps of Engineers. Time and resource constraints did not allow the measurement of intangible assets. Without detailed historical data on these flood related damages it is difficult to incorporate them into the comparative assessment conducted in this report. While some historical data was available (summarized in Section 2.2) it was not detailed enough to generate relationships between flood damages and flood return periods nor did it fully capture the missing components described above. Finally, the analysis assumes no changes to population, increases in urban development, or other changes to social, economic, and spatial configuration of flood vulnerable areas. In other words the analysis holds 2012 conditions constant. While this is an unrealistic assumption, it allows for unbiased inter-temporal comparison.

Next Steps

As a result of the work accomplished, it is recommended that future research explores the public attitudes and preferences for adaptation and minimization of flood risk and vulnerability. It also recommends that future research should explore multi-attribute evaluations of flood management as the Tantramar region continues to improve its understanding of the pressures it faces imposed by a changing climate. As well, it will be important to gain an understanding of the human health and well-being benefits of flood alleviation. Ultimately, however, the Tantramar region needs to develop an integrated strategy that brings together key stakeholders to properly manage flood risks being faced by all stakeholders to ensure both short and long term reductions in flood vulnerability.